1. Field of the Invention
The present invention relates in general to a soldering appliance. More specifically, the present invention is related to a soldering appliance and a voltage regulating circuit to control the heat produced by the element, but it also has a power control circuit that allows the heating element to obtain full heat and then pulses it to maintain the set heat which reduces the power consumption.
2. Description of Related Art
Soldering is the use of a catalytic metal alloy which is liquefied below the workpiece melting point. It is a type of thermal joining process in which the molten filler metal alloy is drawn into a capillary gap between two closely fitting surfaces, sometimes referred to as “sweating” the capillary gap. Soldering is performed at temperatures below 842° F. (450° C.) which is below the melting point of the metals being joined. Solders with melting temperatures below 356° F. (180° C.) are defined as low melting temperature solders, between 392° F. and 446° F. (200° C.-230° C.) are mid range melting temperature solders and high melting temperature between 446° F. and 662° F. (230° C.-350° C.). These are referred to generically as “soft” solders. Intermediate temperature solders, named because it is the intermediate point between soldering and brazing, are any solders which melt above 662° F. (350° C.).
Electrical solder heating appliances allow an operator to apply a controlled application of narrowly directed heat onto a workpiece. Soldering applications include soldering/desoldering electrical components to one another, to printed circuit boards (PCBs), craft applications, and most soldering applications calling for more thermal control than a flame. Solder heating appliances generally take the physical form of a soldering iron, pencil, or “wand”-type, or a soldering “gun”-type appliance. A typical solder heating appliance comprises at least three main parts: the handle/body; the heater; and tip, although the tip may be considered a subpart of the heater. The most common soldering heater appliance is the soldering wand (or iron) which ranges in size from that of a small pencil to the diameter of a broomstick, and larger. Almost all solders are copper tipped, since copper's heat conductivity is extremely high for the cost of copper. The wand-type of solder heating appliance may be connected directly to a power by incorporating essentially all of the electrical components in the interior of the handle/body, or it may be connected to a base unit as part of a “soldering station” where bulkier electrical components are located in a remote base unit or console. Directly powered wand-type solder heating appliances typically utilize a resistive wire heating element (generally coiled) for generating heat. The heating element is positioned adjacent to the tip, thus the tip is indirectly heated by the heating element. Heat is produced by an electrical current flowing through the resistive wire of the coil. Temperatures at the tip may be substantially higher than is necessary for melting solder, but throughput in wand-type appliances with resistive coiled wire elements is generally limited by the amount of heat stored in the mass of the tip and heating element. Wand-type solder heating appliances range from 15 watts (W) to 100 W or more, but are generally wired as “always on” appliances because the slow heat-up characteristics of the coiled resistive wire heating element and their generally poor thermal recovery. U.S. Pat. No. 5,117,091 to Ely titled “Soldering Gun,” which is incorporated herein by reference in its entirety, describes a typical wand-type soldering heating apparatus with an internal resistance heating element encapsulated in a clad iron tube and a removable tip.
Coiled wire heating elements, like most types of solder heating elements, are heated by increasing the amount of kinetic energy of the atoms in the heating coil through the application of an electrical current. The amount of power converted to heat is well understood as being approximately I2R, where I is the current being applied and R is the internal resistance of the coil. The higher the current, the more heat. Furthermore, because the power delivered to the coil is EI, where E is the voltage being applied, the heat generated by the heating element can be substantially increased for the same power by reducing the voltage, E, and proportionally increasing the current, I. However, because step-down transformers are bulky and heavy, most directly wired wand-type appliances use unaltered power directly from the power source. Soldering stations, on the other hand, generally incorporate a transformer, or the like, in the base unit for increasing the current, while stepping down the voltage.
Aside from coil resistive wire heating elements, solder heating appliances make use of other technologies for heating, such as ceramic heating elements. Ceramic heating elements are somewhat more energy efficient than coiled wire elements and are far more temperature responsive. In general, however, they do not have the thermal response necessary for powering them down after each use. Some manufacturers have moved toward extremely lightweight wand-type appliances with extremely narrow tip configuration (pencil irons). These are far more responsive than the coiled wire type element, but due to their low mass, their throughput is often limited.
Solder stations house the heavy and bulky electrical components in a remote base unit so power capacity at the wand can be dramatically increased while actually reducing its weight. Furthermore, solder stations provide the space necessary for incorporating more useful soldering features such as temperature control, continuous solder feeding mechanisms and desoldering vacuum units. Solder stations are especially useful for production work because of their high power capacities and extensive soldering features. An exemplary soldering station is shown in U.S. Pat. No. 3,990,622 to Schurman, Jr. et al. entitled “Apparatus for soldering,” which is incorporated herein by reference in its entirety.
Rarely, if ever, is a wand-type solder heating appliance thermostatically controlled unless it is connected to a soldering station. In general, the power of a wand-type soldering appliance is kept lower to reduce its weight and operating costs. Because most wand-type solder heating appliances are always on when connected to a power source, the superfluous heat is merely exhausted into the ambient environment, resulting in the wand-type appliance being extremely inefficient for its power. Thus, the wand-type solder heating appliance suffers from lower power, and therefore lower work throughput capacity, while simultaneously, suffering higher heat loss and the associated higher operating costs of the appliance.
Most gun-type solder heating appliances use a fast heating, thermally responsive type of heating element, wherein the tip itself, or resistive wire loop, is directly heated by the flow of electrical current through the wire loop. The heating current is trigger controlled and operates at substantially higher wattage than typical wand-type soldering appliances (e.g., 50 W to 150 W gun-type solder heating appliances are common and heavy-duty soldering guns have over 250 W of heating capacity). The wire loop tip generally operates at a much lower voltage than wand-type appliances, between 1 volt (V) and 10 volts, because the total resistance in the wire loop tip is much less than that found in the coiled heating resistive wire element of wand-type solder heating appliances. This is possible because the physical design of the body on a gun-type appliance will accommodate a moderately sized transformer, so stepping up the current is possible. It is also possible to balance the gun such that the added weight of the transformer does not influence soldering.
Heat loss is generally high at the wire loop tip, but also throughout all of the high current electrical components. The I2R losses of low voltage, high current circuit portion of a wire loop-type solder heating appliance are often much higher than the total I2R losses found in the entire electrical circuit of the wand-type. Moreover, the operating power of the gun-type appliance is usually much higher. These losses are ameliorated somewhat by including a trigger switch which the user selects for applying current to the tip, and thereby heating the appliance. Due to the high power output generated from high current and low tip mass, the wire loop tip of gun-type soldering appliances is prone to overheating failures due to the resistive wire loop reaching the point of incandescence. The wire loop may incandesce if left activated for as little as 20 seconds. Current may be applied to the wire loop tip for longer time periods while in continued use, thereby channeling the excess heat into liquefying the solder and keeping the tip just below the point of incandescence. Thus, the gun-type solder heating appliance suffers from proportionally higher external heat losses from the wire loop tip and additional internal I2R losses in the low voltage circuit and the associated higher operating costs, as well as a high incidence of tip failure due to the unregulated overheating of the wire loop tip. Various exemplary embodiments of a gun-type solder heating appliance are described in U.S. Pat. No. 5,569,400 to Lee entitled “Soldering gun with U-shaped insertable terminal structure and tip having differing impedance layers,” as does U.S. Pat. No. 5,477,027 to Biro et al. entitled “Electrical soldering device with a split cylinder transformer secondary,” both of which are incorporated herein by reference in their entireties.
Still another type of solder heating appliance is a desoldering appliance. Desoldering appliances are designed to heat unwanted solder located on the workpiece and extract the solder residue once liquefied. A typical desoldering appliance is shown in U.S. Pat. No. 5,143,272 to Carlomagno et al. entitled “Desoldering device,” which is incorporated herein by reference in its entirety. Desoldering stations often comprise special hollow tip configurations with vacuum assist for extracting or sucking away the unwanted solder, and are commonly referred to as “solder suckers.” The heating element in a solder sucker may be either the coiled resistive wire, ceramic or the resistive wire loop tip and suffers from the identical problems with the corresponding appliances as described above.
Portable solder melting appliances are known in the prior art with battery powered solder heating elements (cordless) which typically comprise coiled resistive wire heating elements. In an effort to extend battery life, cordless solder melting appliances are extremely low power, even less than the wand-type solder heating appliances described above. In fact, aside from a switch for turning, connecting and disconnecting the battery to the heating element, cordless solder melting appliances are very similar in design to the wand-type solder heating appliance and suffer from the identical shortcoming. Additionally, cordless solder melting appliances are severely under-powered.
Prior art solder melting appliances have focused largely on user conveniences and increased throughput without regard to operating efficiencies. One solution for increasing throughput is incorporating a heat sink at or near the tip. The heat sink absorbs latent heat which would otherwise be exhausted to the ambient air when the tip is at higher temperatures, for instance during idle periods when solder is not in contact with the tip, and then releases the heat energy to cold solder when in contact with the tip, such as during active periods when large volumes of solder are being applied to a workpiece. This feature was extremely common in soldering irons which relied on an outside heating source for their heat. However, the larger heat sink usually entails a larger surface to radiate heat into the ambient air, and therefore is usually far less efficient than a comparable solder heating appliance without the heat sink feature.
Another solution, as described above, is to lower the power output of the appliance. While lowering the power output does reduce the total amount of heat being exhausted into the surrounding air, lower throughput results in higher lag times, which in turn increases operating expenses due to the operator's increased idle time. Similarly, other efforts have been directed to reducing the mass of the heating element and tip, thereby increasing thermal response while lowering, somewhat, the power requirement. Each of these alternatives severely lower the appliance's throughput capacity.
Another energy saving measure devised by artisans in the prior art is to insulate the tip of the soldering appliance with a heat resistive thermal insulating cover, sometimes referred to as a “hot iron sock.” Using the hot iron sock effectively is extremely cumbersome for the operator as he must sheathe and unsheathe the iron between uses. This solution has been largely relegated to service people who must move quickly from job to job. With the hot iron sock, they can pack their soldering appliance into a toolbox immediately after the soldering at one job is finished and move on to the next.
Power regulation in the prior art has been limited to switching the current to the heating element on and off. The electrical switching may be manually activated or automated via a temperature sensor such as a bimetal strip switch. U.S. Pat. No. 4,590,363 to Bernard entitled “Circuit for controlling temperature of electric soldering tool,” which is incorporated herein by reference in its entirety, describes an automated switching circuit for controlling power to the heating element of a soldering iron based on a temperature signal received from a thermocouple. While the upper current level may be adjusted, such as for increasing the power output to the heating element, and tip temperature is controlled in prior art soldering appliances by opening the switch to the heating element when the sensed temperature rises above a predetermined temperature level, and closing the switch when the sensed temperature drops below another preset temperature level.